Not Applicable.
The present invention is directed to aqueous fire retardant compositions, and methods of making and using the same, containing dispersed, slurried, or suspended colorants. In particular, the present invention is directed to aqueous fire retardant compositions containing dispersed, slurried or suspended colorants comprised of insoluble, non-fugitive pigments.
A variety of fire retardant solutions are known. xe2x80x9cEvaluation of Megatard 2700: A Proposed New Fire Retardant Systemxe2x80x9d, C. W. George and C. W. Johnson, U.S.D.A. Forest Service, Intermountain Forest and Range Experimental Station, General Technical Report INT-112, August 1981, which is hereby incorporated by reference in its entirety, describes a fire retardant system containing ammonium sulfate as the active fire retardant salt, a guar gum thickener, iron oxide as a colorant, a spoilage inhibitor, and corrosion inhibitors. In this case, the fire retardant composition is prepared by mixing ammonium sulfate and corrosion inhibitor to form a liquid component. The iron oxide, thickener, and spoilage inhibitor are mixed with water to form a slurry. The slurry and the liquid component are then mixed in equal volumes to form the mixed fire retardant, which is then loaded into an aircraft or ground engine, transported to, and applied to retard a wildland fire.
It is conventional practice to add the components of a fire retardant solution, as a preformed concentrate, into water at a prescribed mix (dilution) ratio in order to form the fire retardant solution. There are conventionally three types of fire retardant concentrates: xe2x80x9cdry-powderxe2x80x9d concentrates, xe2x80x9cfluidxe2x80x9d concentrates, and xe2x80x9cliquidxe2x80x9d concentrates.
xe2x80x9cDry-powderxe2x80x9d type concentrates are simply dry mixtures of components that are mixed into water in order to form a fire retardant solution.
The xe2x80x9cfluid concentratexe2x80x9d type fire retardants, which are low viscosity, are delivered to mixing or dilution locations, or depots as low viscosity, concentrated fluids or slurries. When the fluid concentrates are subsequently diluted with water, at their prescribed mix ratios, suspended thickeners are activated and gum-thickened fire retardant solutions are prepared. The level of viscosity obtained upon dilution of the fluid concentrate can be altered by varying the amount of gum-thickener incorporated in the formulation. Fluid concentrate type fire retardants are generally mixed with water at the time of use, directly into the application vehicle. Low viscosity fluid concentrates are formed in accordance with the teachings of U.S. Pat. Nos. 4,839,065, 4,971,728 and 4,983,326, which are hereby incorporated by reference in their entireties.
A third type of wildland fire retardant concentrate, referred to as a xe2x80x9cliquid concentrate,xe2x80x9d is delivered to mixing or dilution locations, or depots as a high viscosity suspension. When the liquid concentrates are subsequently diluted with water, at their prescribed mix ratios, low viscosity fire retardant solutions are obtained. These solutions are formed by dilution prior to use in order to prevent separation and settling of the solids from the liquid. Liquid concentrates are prepared in accordance with the teachings of U.S. Pat. Nos. 3,730,890 and 3,960,735, which are hereby incorporated by reference in their entireties.
Although both xe2x80x9cfluidxe2x80x9d and xe2x80x9cliquidxe2x80x9d type concentrates are fluid or liquid mixtures, the terms have a particular meaning in the art. A fluid concentrate exhibits a low viscosity until diluted with water. At that time, suspended thickeners are activated and the viscosity of the resultant solution remains unaffected, or increases, depending on the amount of thickener in the concentrated composition. A liquid concentrate, on the other hand, is a relatively high viscosity liquid mixture containing suspended clay, and optionally, other components that, upon dilution at the prescribed mix ratio, forms an unthickened fire retardant solution with a reduced viscosity relative to the concentrate form that is prepared. Accordingly, the terms xe2x80x9cliquidxe2x80x9d and xe2x80x9cfluidxe2x80x9d when used in the phrases xe2x80x9cliquid concentratexe2x80x9d and xe2x80x9cfluid concentrate,xe2x80x9d have a specific meaning. When the terms xe2x80x9cliquidxe2x80x9d and xe2x80x9cfluidxe2x80x9d are used elsewhere, they are intended to have their common meaningxe2x80x94referring to the physical phase of matter that conforms to a volume and that is substantially incompressible. Although, as described previously, the terms xe2x80x9cliquidxe2x80x9d and xe2x80x9cfluidxe2x80x9d include mixtures of liquids with undissolved solid particles.
Fire retardant solutions used to combat and control wildland fires are applied from the ground or from the air. Application from the ground is usually from a vehicle such as a fire engine, while application from the air is usually from an airplane or helicopter. It is often desirable to mark the locations where fire retardants have been applied in order to coordinate fire-fighting activities, conserve supplies, and show the progress of the fire-fighting effort. Therefore, color pigments are often added to the fire fighting product at the time of the product""s manufacture.
The fuel that feeds a wildland fire varies widely from grasses to large trees. Therefore, the color pigment in the applied fire retardant must present an adequate color contrast from the background fuel to conveniently show where fire retardant has been applied. The pigmented fire retardants of the prior art, however, might contain too much or too little colorant for a particular application because, while the color and geometry of wildland fuels vary widely, the concentration of pigment is fixed at the time of fire retardant manufacture at the factory.
Accordingly, it would be desirable to have the capability of adjusting the colorant level in the fire retardant solution at the time of use relative to the amount needed to maintain visibility. This ability would both minimize the possibility of leaving unobserved discontinuities in the retardant fire break through which a fire could escape, and minimize the use of colorant in those instances when visibility is easily achieved. Either case would result in savings in cost and possibly property.
In overcoming many of the above disadvantages, a colorized fire retardant composition is provided. In a first aspect of the invention, a colorized fire retardant is provided that comprises an uncolored, or minimally colored fire retardant composition and a colorant in an amount effective to colorize the uncolored fire retardant composition. The colorant of the invention is an aqueous dispersion of a non-fugitive pigment, wherein the aqueous dispersion is a slurry or a suspension, and wherein the pigment is insoluble and has an average particle diameter less than about 1 micrometer.
In a second aspect of the invention, a method of forming a colorized fire retardant is provided that includes adding an aqueous dispersion of a non-fugitive pigment to an uncolored, or minimally colored fire retardant composition in an amount effective to colorize the uncolored fire retardant composition, wherein the pigment is insoluble, the aqueous dispersion is a slurry or suspension, and the aqueous dispersion is added at a time proximate to transporting and discharging the colorized fire retardant composition to a fuel.
In a third aspect of the invention, a method of optically marking fuel is provided that comprises adding an aqueous dispersion of non-fugitive pigments to an uncolored fire retardant composition in an amount effective to colorized the uncolored fire retardant composition, wherein the pigments have an average particle diameter less than about one micrometer, and the aqueous dispersion is a suspension or a slurry that is added at a time proximate to discharging the colorized fire retardant composition to a fuel at a rate effective to colorize the uncolored fire retardant solution. The method further includes discharging the colorized fire retardant solution to form a discharge, directing the discharge to mark the fuel, monitoring a parameter, and adjusting the rate that the pigment is added responsively to the monitored parameter.
Not applicable.
The fire retardant compositions of the present invention include an uncolored or minimally colored fire retardant composition and a colorant that, in combination, form a colorized fire retardant composition. As used herein, the term xe2x80x9cuncoloredxe2x80x9d includes both minimally uncolored and truly uncolored. Accordingly, xe2x80x9cuncolored fire retardant compositionsxe2x80x9d include minimally colored fire retardant compositions. The uncolored fire retardant compositions of the invention can also be solutions, mixtures, emulsions, or suspensions. The colorant of the invention is present in an amount effective to colorize the uncolored fire retardant composition, and includes an aqueous dispersion of an insoluble, non-fugitive pigment. The aqueous dispersion is a slurry or a suspension. As used herein, the term xe2x80x9caqueousxe2x80x9d means made of, by, or including water. As such, an aqueous solution may contain other solvents, such as alcohol and/or glycol.
Although the term xe2x80x9cfire retardant solutionxe2x80x9d is used herein, it is understood that such fire retardant liquid mixtures are not true solutions in which all of the components are dissolved to form a single homogenous liquid phase without solid phases or other immiscible liquid phases present. It will be recognized that some of the components used may be essentially insoluble in the liquid components. That is, components such as iron oxide and titanium oxide are insoluble in water. Nonetheless, the term xe2x80x9csolutionxe2x80x9d will be used as well as the more physicochemically correct terms such as xe2x80x9cfluidxe2x80x9d or xe2x80x9cliquidxe2x80x9d because the term is commonly used in this art. Thus, the term xe2x80x9cfire retardant solutionxe2x80x9d is used to mean the fire retardant composition formed by water and other liquid and/or solid components ready for application onto burning fuels.
The pigments of the invention have properties effective to allow them to be dispersed in water to form the aqueous pigment dispersion and to cause the aqueous pigment dispersion to remain stable, resisting sedimentation without agitation, until the dispersion is used to form colorized fire retardant liquids. The term xe2x80x9cpigmentxe2x80x9d as used herein, means colorizing compounds that are insoluble in the media in which they are used, and, consequently are present as solid particles. The terms xe2x80x9cdispersionxe2x80x9d and xe2x80x9csuspensionxe2x80x9d as used herein mean solid/liquid mixtures in which the solid does not readily separate out from the liquid prior to the use of the dispersion or suspension, even in the absence of agitation or some other energy being imparted to the dispersion. The liquid can include some dissolved solids, but generally includes only liquids containing insoluble solids. The term xe2x80x9cslurryxe2x80x9d as used herein means a solid/liquid mixture in which the solid separates out from the liquid in the absence of agitation or some other energy being imparted to the mixture. It is understood by one of ordinary skill in the art that, other parameters being equal, slurries are formed by larger sized particles than the smaller sized particles that form dispersions or suspensions.
The colorant of the invention is comprised of a non-fugitive pigment. The non-fugitive pigment is one that is insoluble in a carrier liquid, and which, if colored, does not necessarily fade after aerial application of the fire retardant composition. The non-fugitive pigment is dispersible in the slurry or suspended colorant of the invention. Any non-fugitive pigment can be employed in the compositions of the invention. Suitable non-fugitive pigments include, but are not limited to iron oxides, including red and yellow iron oxide, as well as titanium dioxide, a white pigment, antimony oxide, potassium titanate, ferrite, and iron cyanide blue. Other suitable non-fugitive pigments are found in Pigment Handbook, Volume 1, Properties and Economics, edited by Temple C. Patton, which is hereby incorporated by reference in its entirety. The same can be used as opacifying agents in accordance with the invention. Opacity is defined as the ability of matter to obstruct the transmission of radiant energy or light. Accordingly, non-fugitive pigments, which do not fade upon exposure to light, may also be useful as opacifying agents. In a specific embodiment of the invention, red iron oxide is employed as the non-fugitive pigment. In another specific embodiment of the invention, titanium dioxide is the non-fugitive pigment of the invention. Combinations of non-fugitive pigments are employed in yet another embodiment of the invention.
Aqueous pigment dispersion colorants, being already dispersed, are more easily dispersed in a fire retardant solution than are dry-powder pigment colorants. Without being bound by theory, this difference in the ease of dispersion is believed to result from the fact that the pigment particles are present in the aqueous pigment dispersions as individual, discrete and separate particles whereas the dry-powder pigments tend to exist in the dry state as agglomerates. Such agglomerates require considerable energy input to achieve the same degree of ultimate dispersion as the pre-dispersed pigments in the aqueous pigment dispersions.
Accordingly, the colorant component of the present invention, which are aqueously suspended or slurried pigments, can be advantageously added directly to a neat fire retardant solution, in order to form the colorized fire retardant solution of the present invention, at any time before applying the colorized fire retardant solution to a fire or to fuel threatened by a fire. It is particularly advantageous to add the aqueously slurried or suspended colorant shortly before the thus formed colorized fire retardant solution is used, such as at the time that the delivery (or application) vehicle is being loaded with the fire retardant solution, or just before, or as the colorized fire retardant is discharged to the fuel.
The colorized fire retardant solutions of the present invention are sufficiently stable from settling or separation of the dispersed pigment from the liquid so that the colorized fire retardant solutions can be mixed ahead of the time of use. In particular, the viscosity stability during storage may be improved when the aqueous pigment dispersion is present.
The present invention, as described above, utilizes insoluble, non-fugitive pigment particles that are dispersed in an aqueous medium as a slurry, suspension, or dispersion. The suspended colorant is of a particle size effective to maintain the dispersion of the pigment particles, with little or no agitation, prior to use of the dispersion. By contrast, agitation is required when pigment slurries of the invention are used, without which the solid particles would settle out from the liquid prior to using the slurry. The average particle size of the insoluble, non-fugitive particles used to form the aqueous pigment dispersion colorant of the invention is less than about 10 micro-meters (xcexcm), preferably less than about 5 xcexcm, and more preferably less than about 1 xcexcm. The smaller size particles are more effective at remaining dispersed or suspended in an aqueous medium, e.g. water, without settling, when agitation or other energy is not imparted.
In one embodiment, the average particle size is in the range of about 0.35 xcexcm to about 0.55 xcexcm. In another embodiment, the average particle size is in the range of about 0.35 xcexcm to about 0.45 xcexcm. As stated above, small particle size distribution causes the slurry, dispersion, or suspension to be better dispersed or suspended in the aqueous carrier.
As will be readily understood by one skilled in the art, the pigments used in the aqueous pigment dispersion colorant of this invention can be produced by any convenient method known to produce small particles that will remain in a dispersion, slurry, or suspension. For example, solid pigments can be ground to form appropriately sized particles.
It is important that the pigments of the invention remain dispersed as a dispersion, slurry, or suspension. Accordingly, constituents that cause agglomeration should not be included. For example, the presence of attapulgus clay in some fire retardant solutions leads to the agglomeration of some pigment dispersions. It is understood that it is the agglomeration that should be avoided rather than any particular ingredient. Thus, any potential agglomerating ingredient should be counteracted by any convenient effective dispersing ingredient such as, for example, a dispersing agent or a surfactant.
The colorant of the invention can include opacifiers (hiding agents) such as, for example, potassium titanate, zinc oxide, zinc sulfide, lead salts, antimony oxide, earth-tone colored iron oxides, iron phosphates and the like, and selected extender or filler pigments such as non-reactive clays, calcium sulfate and mixtures thereof at a level effective to provide a desired amount of opacity. Such components can be incorporated by any convenient method. The opacifier can be any hiding pigment or any filler powder that (i) is insoluble and non-reactive in the fire retardant solution and (ii) becomes acceptably inconspicuous after the application of the fire retardant solution. It is preferred that the opacifier is able to opacify or hide the substrate without causing significant abnormal colors relative to the applied environment. Thus, for applications to forest fires, an earth tone would be desirable as a background color to which the colorized liquid fades. Such earth tones can be formed by using brown iron oxide with a white pigment to lighten the brown color as desired to blend with the background color of the area of dispersal as the fugitive color fades. Such components may also be conveniently included in the uncolored fire retardant compositions.
One embodiment of the present invention is directed to forming a colorized fire retardant composition from an uncolored fire retardant composition. The method comprises adding the above-described colorants of the invention, which are aqueous dispersions of insoluble, non-fugitive pigments to the uncolored fire retardant solution in an amount effective to colorize the uncolored fire retardant composition. The colorant is added at a time proximate to discharging the colorized fire retardant composition to a fuel.
The method can include monitoring at least one parameter and adjusting the amount of aqueous pigment dispersion incrementally in response to the monitored parameter. The parameter monitored can be any conveniently measured property such as the color or reflectance of the fuel, color of the colorized fire retardant solution, wind conditions, ambient temperature, or the temperature or smoking character of the fire. The amount of aqueous pigment dispersion can be added incrementally, at a rate effective to colorize the uncolored fire retardant solution, as the colorized fire retardant solution is loaded onto the applying vehicle or, possibly, as it is discharged onto the target fuel. The rate can be adjusted in response to the monitored parameter.
Another embodiment of the present invention is directed to optically marking fuel. The method comprises adding the above-described colorants of the invention to uncolored fire retardant solutions at a rate effective to colorize the uncolored fire retardant solutions; discharging the colorized fire retardant solutions to form a discharge; directing the discharge to mark the fuel; monitoring at least one, above-described parameter; and adjusting the rate that the pigment is added responsively to the monitored parameter.
The color properties of the fire retardant compositions of the present invention increase with applied film thickness. The opacity, transmitted color intensity of the wet film, and reflected color intensity of the dry film increase with coverage level. The fire retardant compositions of the invention provide effective visibility at the coverage levels typically required in the field. For example, fire retardant coverage levels of the present invention are in the range of about 2 gpc to about 4 gpc (gallons per hundred square feet). The following examples illustrate specific embodiments of the invention without limiting the scope of the invention in any way.